Investments - Holding gains (losses) on equity securities still held (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2026 |
Sep. 30, 2025 |
Sep. 30, 2026 |
Sep. 30, 2025 |
|
| Holding Gains (Losses) on Equity Securities Still Held [Line Items] | ||||
| Holding gains (losses) on equity securities | $ (10) | $ 2 | $ (2) | $ 22 |
| Income Statement Location [Axis]: us-gaap:DebtAndEquitySecuritiesRealizedGainLoss | ||||
| Holding Gains (Losses) on Equity Securities Still Held [Line Items] | ||||
| Holding gains (losses) on equity securities | (8) | 7 | 9 | 24 |
| Income Statement Location [Axis]: us-gaap:NetInvestmentIncome | ||||
| Holding Gains (Losses) on Equity Securities Still Held [Line Items] | ||||
| Holding gains (losses) on equity securities | $ (2) | $ (5) | $ (11) | $ (2) |